Thermo-stabilized copolymers of trioxane with urea compounds



copolymers as well as the homopolymers against thermal degradation and oxidation. It is surprising that the stabilizers used for stabilizing the homopolymers of trioxane cannot be used in the same manner for stabilizing the o Unlted States Patent ce Patented Apr. 25, 1967 l 2 3 316 206 copolymers. In many cases the stabilizers for homopolymers show no or only a little eltect on copolymers, more Ifrequently, however, it is just thecpposite. It is particu- Hans Dieter Hermann, Edgar Fischer, and Giinther Roos, arly f F that the Stablhzer combm'fltKons used F kf t am Main, Germany, assignors to FarbWel-kev 5 for stabilizing copolymers show strong synerglstlc etfects. H h t Akfl ge efl h ft vormals M i L i & Therefore, it is important always to use harmonized stabi- Bruning, Frankfurt am Main, Germany, a corporation lizer combinations, one component of which mainly prov of Germany tects the copolymer against thermal degradation and the p g Filed P 274,813 other mainly against oxidation. Urea compounds are Claims priority, application Ggrmany, Apr. 28, 1962, known as stabilizers for homopolymers of formaldehyde. However, in the stabilization of the homopolymers, poly- 3 260458) amides and amides of polybasic carboxylic acids have a The present invention relates to a process for stabilizing better effect for stabilizing oxymethylene copolymers, copolymers of trioxane of high molecular weight by inamidines have been proposed as stabi izers. n y corporating into the copolymers N-substituted urea decases, h w v their effect is not sufiicient and, morerivatives. over, they have the tendency to cause cross-linking of the Recently, thermally stable polyoxymethylenes of high P y molecular weight have gained considerabletechnical im- It has now been found that OXymethyleHe copolymers portance. They are excellently suitable for the manufachaving oxalkylene groups with 2 or 4 adjacent carbon ture of shaped articles by the injection molding or exatoms in the main chain, which chain may carry as subtrusion processes. The shaped articles are characterized stituents lower alkyl groups, can be stabilized by N-subespecially by their hardness, strength and toughness. The stituted urea derivatives. There are preferably used urea two most important processes for the manufacture of polyderivatives carrying at least one substituent at the nitrogen oxymethylenes are the anionic polymerization of formalom, aid su s it ent having an amino group and being dehyde and the cationic polymerization of trioxane. The selected from the group consisting of an aliphatic alkyl polyoxymethylene prepared in this manner carry hydroxy radical having 1 to 18 carbon atoms, a cycloaliphatic hygroups at the chain ends and have, thus, a semiacetal drocarbon radical having 5 to 6 carbon atoms, a monostructure. Under the action of heat the semiacetals deto binuclear aromatic hydrocarbon radical and a heterocompose with the formation of monomeric formaldehyde. cyclic hydrocarbon radical. An especially good effect can According to a so-called zipper reaction, this decomposibe achieved when the aforesaid compounds are used in tion can lead to the quantitive disintegration of the polycombination with phenols and/ or aromatic amines already mers into monomeric formaldehyde. known as stabilizers for trioxane and the copolymers Polyoxymethylenes which are subjected to the action of thereof. Urea derivatives as specified above, which, heat should, therefore, be free from terminal semiacetal owing to their alkalinity, have no or only a poor stabilizgroups. Various methods are known for blocking the ing effect on poloxymethylene acetates, are distinctly suchain ends of the polymers, but all these methods are more perior to polyamides, amides of polybasic carboxylic acids or less complicated and expensive. The best known and amidines when used as stabilizers for oxymethylene method is the acetylation of the terminal hydroxy groups copolymers. with acetic anhydride. After the reaction the acetic an- Suitable urea derivatives are, for example: N,N'-bis-(lhydride in excess and the acetic acid formed must be 40 aminoethyl)-urea, 2-amino-4-ureido butyric acid ethyl carefully removed from the polymer. The polyoxyester, bis-(ureidomethyDamine, tris-(ureidfomethyl)amine, methylene acetate thus obtained has a satisfactory stability dipropylene-triamine-diurea, N-bis-(ureidoethyl)-2-nitril0- in the heat, but it issensitive not only to the action of ethylamine, 2,4-bis-ureido-diphenylamine, N-bis-(ureidoacids but also to the action of alkalies. ethyl)-2-nitrilooctadecylamine 1,6-bis-(2-pyridylcarboxy- Methods for etherifying the terminal groups are comureido)-hexamethylene. plicated, partially they give poor yields and the products An optimum stabilizing elfect is obtained when the obtained have a low molecular weight. aforesaid urea derivatives are used together with phenols, It is much simpler to produce oxymethlene copolymers (for example the phenols defined in US. Patent 2,871,- with stable terminal groups. By a suitable selection of 220) and/or aromatic amines (for example the amines the comonomers, copolymers can be obtained in which define-d in US. Patent 2,920,059), which have already the disintegration starting at the chain ends comes to 21 been proposed for stabilizing homopolymers of trioxane. standstill at the structural units of the comonomers. For Suitable phenols are especially those which carry, as subpreparing a stable copolymer it is thus only necessary to stituents in ortho and para position to the phenolic hysubject the copolymer to a thermal or alkaline aftertreatdroxy group, aliphatic hydrocarbon radicals having 1-18 ment. Especially favorable oxymethylene copolymers are carbon atoms, for example, 2-methyl-4-tert. butyl 6-octathose which contain in the chain oxalkyl groups having decyl phenol. Particularly suitable are bisphenols, for at least two adjacent carbon atoms. They can be prepared example 2,2-methyl-bis-(4-methyl-6-tert.butyl phenol) or quite easily, for example, by copolymerizing t-rioxane with condensation products from a phenol substituted in para cyclic others or formals. position by a low molecular weight aliphatic hydrocarbon In practice, it is necessary to stabilize the oxymethylene radical and formaldehyde, for example the condensation product from 4-tert.butyl phenol and formaldehyde.

Amines having a good stabilizing effect are, for example the derivatives of diphenyl amine, such as 4,4-

dioctyldiphenyl amine. Furthermore, there are well suitable aromatic amines carrying as substituents besides the amino-group, phenolic hydroxyl groups or amide groups or urea groups.

The above-mentioned stabilizer combinations confer complex compounds thereof as catalysts. Comonomers which are especially suitable for the manufacture of the copolymers are cyclic alkylene oxides preferably having 2 to 4 carbon atoms and the derivatives thereof, oxetanes upon the oxymethylene copolymers a thermal stability 5 and cyclic formals of, for example, glycol, 1,3-butanenot previously reached at a processing temperature in diol and 1,4-butane-diol, diethylene glycol or 1,4-butenethe range of about 190 to 250 C. and an outstanding diol-(2). In some cases it may be advisable to incorstability to oxygen. The combinations are very easy porate further stabilizers into the copolymer, for exto use. In most cases it is sufiicient to mechanically mix ample amides of polybasic carboxylic acids, polyamides them with the copolymer. However, they can be apor compounds of bivalent sulfur. In any case, it is plied to the polymer in any other manner. favorable to use additionally a light stabilizer, for ex- The stabilizer concentration required for improving ample an u-hydroxybenzophenone. the thermal stability of high molecular weight oxymethyl- The stabilizer system can be incorporated into the ene copolymers depends on the activity of the urea compolymer in any known manner. Particularly suitable pound, the phenol and/or aromatic amine used and, are methods which allow of auniform distribution of the moreover, on the type and the quality of the copolymer finely divided stabilizers in the copolymer. For example, to be stabilized. Thus the concentration can vary within the finely ground stabilizers can be incorporated into the wide limits. Each component of the stabilizer system can copolymer of high molecular weight in a dry mixer or on be used in a concentration in the range of from 0.01 a roll mill. Alternatively, the stabilizers can be disto 10% by weight, calculated on the polymer, and pref solved in a solvent, for example methanol and acetone, erably 0.05 to 5% by weight. the polymer can be suspended in the solution obtained For testing the thermal stability of the oxymethyle e and the solvent can be evaporated until the mixture is copolymers, samples with and without stabilizers were rysometimes, i may be especially favorable to inheated for a definite period of time at a temperature corporate the stabilizer system into the melt of the coabove 200 C., for example for 30 minutes at 220 C. polymer. -In this case labile polymer constituents may and the loss in weight was determined. The tests were be m nat dcarried out in an inert atmosphere, for example under The g moleelllaf Weight 0Xymethylene copolymers nitrogen, and in air or oxygen. A satisfactory stabilizer Which have been Stabilized y Process of the Present system must give good values under the most different invention can he used, Particularly When y Contain conditions. stable terminal groups, for the manufacture of fibers, By oxymethylene copolymers there are to b d foils and films and, moreover, for making tubes, profiles stood those which contain in the main chain oxalkyl and injection molded aftielee groups having 2 to 4 adjacent carbon atoms i an The following examples serve to illustrate the invenamount of 0.1 to 50% by weight, calculated on the total tion but they are not intended limit it thereto, the copolymer, h copolymers need not contain stablfi percentages being by weight unless otherwise stated. terminal groups. Terminal semiacetal groups can be E l 1 eliminated from the copolymer after the incorporation of the stabilizer system, for example by kneading the j ig i of tlnoiiane and 4% by polymer at 180-220 C. under reduced pressure. In lg o i yene gyco o-rma1 Winch was free from many cases it is more suitable however to stabilize counstable port-1ons was mechamcauy mlxed 1th the pol mers havino Stable terminal Th bT pounds specified in Table 1. The stabilized samples y a p e P} 11ers were then heated for minutes at 230 C. in air. The aeeoldlhg t0 e lnventlon can e e stablhllhg all loss in weight of the samples is indicated in Table l. p y h haylhgo fedheed vlseoslty h than The test results show that the compounds of the invendetermined at 140 C. with a 0.5% solution of the poly- 45 tion are superior to poly-N-vinyl-ethyl-acetamide and a rner in butyrolactone 1n the presence of 2% of diphenylknown urea derivative.

TABLE 1 Loss in weight Stabilizerl Percent Stabilizer2 Percent whz n h a fi ior 45 minutes at 230O.in air 4,4 dioetyldiphcnylamine 0. 5 3. 25

0.5 L OONH-O O-NH-CHr-CHr-CHr 2 1 1,20

0. 5 N-bis-ureido-ethyl-2-nitrilo-ethylamine 1 1. 07

0. 5 Poly-N-vinyl-ethyl-acetamide 1 2. 28

0. 5 Urea carboxylic acid ethyl ester 1 2. 48

amine. Polymers having a reduced viscosity in the range of from 0.5 to 2 are preferably used. Although, on principle, all oxymethylene copolymers having a reduced viscosity within the specified limits can be stabilized, it is advantageous to use copolymers already having a certain minimum stability, for example copolymers which lose at most 80% of their weight when heated for 30 minutes at 220 C.

oxymethylene copolymers of high molecular weight can be readily produced by cationic polymerization, preferably in the presence of boron tri-fluoride and the Example 2 The stabilizers specified in Table 2 were dissolved in methanol. In the solutions there was suspended each time a high molecular weight copolymer of trioxane and 2% ethylene oxide having stable terminal groups. The solvent was then evaporated while stirring until the mixture was dry.

The stability of the samples was tested under the conditions set forth in the following Table 2. Table 2 likewise illustrates the superiority of the claimed stabilizer combinations over known compounds.

TABLE 2 Percent; loss in weight of sample after p ating for- Stabrhzer 1 Percent Stabilizer 2 Percent 90220 O. 45230" O. 45230 C. under N 2 under air under 2,2-methylene-bis (at-methyl-fi-t.

butylphenol 10. 7 23. 0 45. 0 Do 1 6.1 2.2 8.1 Do. 1 Dipropylenetriamine diurea 1 1. 9 1. 65 4. 9 Do- 1 N-b1s-ureidoethyl-$-nitri1oethylamine 1 1. 4 l. 45 2. 9

Do 1 N -CONILC O-NIi-CI'IrCHz-Cflz 2 1 1.5 1.29 3.3

Condensation product from pisobornyl-phenol-l-C H20. 1 N C O NHC O-NH-C Hz-C Hz-C Hz 3. 2. 1 11. 2

Do 1 Dipropylenetriamine diurea 1 1. 9 1. 48 6. 0 Do 1 N-biS-ureidoetllyl-2-nitriloethylamine 1 1. 3 1. 13 2. 3 2, 2-methylene-bis (4-methyll N N -diphe11yl urea. 1 3. 5 2. O7 6. 5

butylphenol) D0- 1 Urea 1 5.1 2.21 7.0 1 Malonic acid diam 1 4. 1 2. 13 8.2 1 Melamine 1 3. 1 1. 85 6. 5

Example 3 The compounds mentioned in Table 3 were mechanically incorporated into an acetylized homopolymer of trioxane and the loss in weight of the samples was determined after heating for minutes at 220 C. under nitrogen. The table shows that the stabilizer combinations have a low synergistic effect on homopolymers (ureidomethyl) amine, dipropylene-triamine-diurea, N- bis-(ureidoethyl)-2 nitriloethylamine, 2,4-bis-ureidodiphenylamine, N-bis-(ureidoethyl) Z-nitrilo-octadecylamine or 1,6-bis-(2-pyridylcarbonylureido)-hexamethylene.

2. A copolymer of trioxane and diethylene glycol formal or ethylene oxide in intimate admixture with from of trioxane and that a compound claimed as stabilizer 10% y Weight of y for trioxane copolymers has a poor stabilizing effect on 40 urea, 2-am1no-2-ure1dobutyr1c acid ester, bis-(ureidotrioxane homopolymers. methyl)-amine, tris-(ureidomethyl)-amine, dipropylene- TABLE 3 Percent loss weight of Stabilizer 1 Percent Stabilizer 2 Percent sample after heating for 30 min. at 220 C. under N Malonic acid diamide 1 3.7 Do 1 3.8 Methoxymethyl polycaprolactarn 1 3. 2 Urea carboxylic acid ethyl ester 1 6. 2 N-bisureidoethyl-2-nitriloethylamine. 1 10. 2 D0 l 2,2-rnethylene-bis-(4-methy .butylpl1enol) 8.2

Example 4 1% of 2,2-methylene-bis-(4-methyl-6-tert. butylphenol) was kneaded for 10 minutes at 200 C. into the melt of a copolymer of trioxane and 5% of dioxolane. When heated for minutes at 230 C. in air a sample lost 2.20% of its Weight. A further sample into which, besides the bisphenol, 1% of 2,4-bisureidodiphenylaminc had been incorporated by kneading lost only 0.82% of its Weight when heated in air for 45 minutes at 230 C.

We claim:

1. A copolymer whose repeating units consist essentially of OCH groups interspersed with 0.1 to by weight of OCH CH -(R groups in which R is selected from the group alkyl-substituted methylene and lower alkyl-substituted oxymethylene radicals and n is 0 to 2, said copolymer being in intimate admixture with from 0.01 to 10% by weight of N,N-bis-(l-aminoethyl) urea, 2-amino-2- ureidobutyric acid ester, bis-(ureidomethyl)-amine, trisconsisting of methylene, lower triamine-diurea, N-bis-(ureidoethyl)-2-nitriloethylamine, 2,4-bis-ureido-diphenylamine, N-bis (ureidoethy1)-2-nitrilo-octadecylamine or 1,6-bis-(Z-pyridylcarbonylureido)- hexamethylene.

3. A coploymer of trioxane and diethylene glycol formal or ethylene oxide in intimate admixture with from 0.01 to 10% by Weight of N,N'-bis-(l-aminoethyl)-urea, 2-amino-2-ureidobutyric acid ester, bis-(ureidomethyl)- amine, tris-(ureidornethyl)-amine, dipropylene-triaminediurea, N-bis-(ureidomethyl)-2-nitriloethylamine, 2,4-bisureido-diphenylamine, N-bis-(ureidoethyl)-2-nitrilo-octadecylamine or 1,6-bis-(2- pyridylcarbonylureido)4hexamethylene and from 0.01 to 10% by weight of an additional stabilizer selected from the group consisting of 2,6-dimethyl-4-tert. butyl phenol, 2,2-methylene-bis-(4- methyl-6-tert. butyl phenol) and the condensation products of p-isobornyl phenol or 4-tert. butyl phenol and formaldehyde.

(References on following page) References Cited by the Examiner UNITED STATES PATENTS Hill 260-459 Kabico et a1. 260-459 Dolce et a1. 260-459 Hermann et a1 260-459 Kray et a1. 260-459 Eguchi et a1 260-45 .9

8 3,201,367 8/1965 Smith 260-459 3,240,748 3/1966 Schmidt et a1. 260-45.95

FOREIGN PATENTS 216,218 7/1961 Austria.

LEON J. BERCOVITZ, Primary Examiner.

H. E. TAYLOR, Assistant Examiner. 

1. A COPOLYMER WHOSE REPEATING UNITS CONSIST ESSENTIALLY OF -OCH2- GROUPS INTERSPERSED WITH 0.1 TO 50% BY WEIGHT OF -OCH2CH2-(R3)N- GROUPS IN WHICH R3 IS SELECTED FROM THE GROUP CONSISTING OF METHYLENE, LOWER ALKYL-SUBSTITUTED METHYLENE AND LOWER ALKYL-SUBSTITUTED OXYMETHYLENE RADICALS AND N IS 0 TO 2, SAID COPOLYMER BEING IN INTIMATE ADMIXTURE WITH FROM 0.01 TO 10% BY WEIGHT OF N,N''-BIS-(1--AMINOETHYL) - UREA, 2-AMINO-2UREIDOBUTYRIC ACID ESTER, BIS-(UREIDOMETHYL)-AMINE, TRIS(UREIDOMETHYL) - AMINE, DIPROPYLENE-TRIAMINE-DIUREA, NBIS-(UREIDOETHYL)-2 - NITRILOETHYLAMINE, 2,4-BIS-UREIDODIPHENYLAMINE, N-BIS-(UREIDOETHYL) - 2 - NITRILO-OCTADECYLAMINE OR 1,6-BIS-(2-PYRIDYLCARBONYLUREIDO)-HEXAMETHYLENE. 